Update package.json

[alinaimi]

covering more extensions

[mfloto]

Apparently .sl3 is also an associated extension.

[turbotimon]

@judemont @alinaimi Is there something preventing this merge? I like the simplicity and clean UI of this extension. However my sqlite DBs have also often a .db ending for compatibility with other tools. So I really would like to have this option.

If merge is ok, the README should be updated accordingly.

As other databases than sqlite sometimes also use .db ending, we could check the Magic Header String (see 1.3.1) of a .db file (or in general for all files): "SQLite format 3\000"

[qwtel]

I've manually added this in v0.4.0+